The symptoms of exposure to low levels of carbon monoxide can be similar to those of food poisoning and flu. But unlike flu, carbon monoxide poisoning doesn't cause a high temperature (fever).

The symptoms can gradually get worse with prolonged exposure to carbon monoxide, leading to a delay in diagnosis.

Your symptoms may be less severe when you're away from the source of the carbon monoxide. If this is the case you should investigate the possibility of a carbon monoxide leak, and ask a suitably qualified professional to check any appliances you think may be faulty and leaking gas.

The longer you inhale the gas, the worse your symptoms will be. You may lose balance, vision and memory and, eventually, you may lose consciousness. This can happen within two hours if there's a lot of carbon monoxide in the air.

Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, such as difficulty thinking or concentrating and frequent emotional changes – for example, becoming easily irritated, depressed or making impulsive or irrational decisions.

Breathing in high levels of carbon monoxide gas can cause more severe symptoms. These may include:

impaired mental state and personality changes (intoxication)

vertigo – the feeling that you or the environment around you is spinning

ataxia – loss of physical co-ordination caused by underlying damage to the brain and nervous system

breathlessness and tachycardia (a heart rate of more than 100 beats per minute)

What causes carbon monoxide to leak?

Gas, oil, coal and wood are sources of fuel used in many household appliances, including:

boilers

gas fires

central heating systems

water heaters

cookers

open fires

Incorrectly installed, poorly maintained or poorly ventilated household appliances – such as cookers, heaters and central heating boilers – are the most common causes of accidental exposure to carbon monoxide.

The risk of exposure to carbon monoxide from portable devices may also be higher in caravans, boats and mobile homes.

Your symptoms will often indicate whether you have carbon monoxide poisoning, but a blood test will confirm the amount of carboxyhaemoglobin in your blood. A level of 30% indicates severe exposure.

People who smoke can often have higher than normal levels of carboxyhaemoglobin in their blood, which can sometimes make it difficult to interpret the results.

Mild carbon monoxide poisoning doesn't usually need hospital treatment, but it's still important that you seek medical advice.

Your house will also need to be checked for safety before anyone returns. Read more about what to do if you suspect a leak.

Standard oxygen therapy

Standard oxygen therapy in hospital will be needed if you've been exposed to a high level of carbon monoxide, or you have symptoms that suggest exposure.

You'll be given 100% oxygen through a tight-fitting mask (normal air contains around 21% oxygen). Breathing in concentrated oxygen enables your body to quickly replace carboxyhaemoglobin. Therapy will continue until your carboxyhaemoglobin levels decrease to less than 10%.

HBOT may be recommended in certain situations – for example, if there's been extensive exposure to carbon monoxide and nerve damage is suspected. The use of HBOT will be decided on a case-by-case basis.

Recovery

The length of time it takes to recover from carbon monoxide poisoning will depend on how much carbon monoxide you've been exposed to and how long you've been exposed to it.

Complications of carbon monoxide poisoning

Prolonged significant exposure to carbon monoxide can cause serious complications, including brain damage and heart problems. In very severe cases, it can result in death.

Effects of severe carbon monoxide poisoning include:

breathlessness

chest pains

seizures (fits)

loss of consciousness

Around 10-15% of people who have severe carbon monoxide poisoning develop long-term complications.

Brain damage

Prolonged exposure to carbon monoxide can cause memory problems and difficulty concentrating. It can also cause vision loss and hearing loss.

In rare cases, severe carbon monoxide poisoning can cause Parkinsonism, which is characterised by tremors, stiffness and slow movement.

Parkinsonism isn't the same as Parkinson's disease, which is a degenerative neurological condition linked to ageing.

Heart disease

Coronary heart disease is another serious condition that can develop as a result of long-term carbon monoxide exposure.

Coronary heart disease is where the heart's blood supply is blocked or interrupted by a build-up of fatty substances (atheroma) in the coronary arteries.

If the blood supply is restricted, it can cause angina (chest pains). If the coronary arteries become completely blocked, it can cause a heart attack.

Harm to unborn babies

Long-term exposure to carbon monoxide gas can also damage an unborn baby. Babies exposed to carbon monoxide during pregnancy are at risk of:

low birth weight

perinatal death (stillbirth and death that occurs within the first four weeks of birth)

behavioural problems

Preventing carbon monoxide poisoning

It's important to be aware of the dangers and identify any appliances in your house that could potentially leak carbon monoxide.

Maintaining and servicing appliances

Boilers, cookers, heating systems and appliances should be installed and regularly serviced by a reputable, registered engineer. Don't attempt to install or service appliances yourself.

Anyone carrying out work on installations and appliances in your home must be registered with a relevant association, such as the: